The present invention relates to orthopaedic devices, and, in particular, to an orthopaedic device for providing improved mechanical coupling to a longitudinally extending surgical rod.
The use of elongated, cylindrical surgical rods in the treatment of the diseases of the spine, such as scoliosis, kyphosis, and instability, is well-known in the medical arts. Such rods, known as spinal rods, achieve rigid spinal fixation when mechanically coupled to bone anchor attachments or elements. These rods are available in a variety of diameters, lengths and surface characteristics. Certain of these surgical rods are threaded along their length while others are smooth, notched, or ratcheted. One style is provided with a "diamond-cut" or diamond shaped surface over its entire length.
These longitudinally extending surgical rods are used, generally, in pairs placed on the posterior surface of the left and right sides of the lamina of the human spine. Such rods are mechanically secured at selected locations of the vertebrae of the spine by anchor attachments or elements, i.e., hooks or screws.
One example of a widely used anchor attachment member is the conventional orthopaedic hook having a block-shaped head portion, with a central, cylindrical bore therethrough, and a hook portion. The bore of the orthopaedic hook is slidably positioned over the surface of the surgical rod to the selected location for attachment. The hook portion may have a variety of different shapes, lengths and openings for attachment to specific anatomical sites of the vertebra. When the anatomical site has been determined and the hook portion anchored, the conventional orthopaedic hook is locked to the surgical rod either by ratchet or by one or more setscrews located within the block-shaped head portion.
One type of orthopaedic screw, used as an anchor attachment member, has a block-shaped head with cylindrical bore therethrough for slidable positioning over the surface of the surgical rod to the selected anatomical site. The shank and threaded end of this orthopaedic screw extends perpendicularly from the axis of the cylindrical bore. After the threaded end of the screw is mechanically attached, as in vertebra or pelvic fixation, the screw is retained in position on the surgical rod by one or more setscrews in the head of the screw.
Another anchor attachment element known in the medical art is the eyebolt. This element is a short machine screw with a relatively large block head having a cylindrical bore therethrough, the axis of the bore being perpendicular to the axis of the screw. Like the orthopaedic screw, the cylindrical bore of the eyebolt receives the surgical rod enabling the eyebolt to be slidably positioned along the rod. The eyebolt is used together with a hook member provided with a block-shaped head portion having a pair of mutually perpendicular open yoke portions. The head of the eyebolt, with surgical rod therein, is placed within the first of the open yoke portions while the threaded portion of the eyebolt is placed within the second open yoke portion. The first open yoke portion straddles both the head of the eyebolt and the portion of the surgical rod adjacent each side of the head. The second open yoke portion straddles the threaded portion of the eyebolt. An advancing nut on the threaded end of the eyebolt causes a surface portion of the cylindrical surgical rod adjacent each side of the head of the eyebolt to be drawn into physical contact with a portion of the inner surface of the first open yoke member for friction engagement therebetween. In this manner, the hook member is held in a relatively fixed position with respect to the surgical rod.
The conventional orthopaedic devices, with their closed-bore, block-shaped heads, whether hooks or screws, are extremely difficult to install between the selected anatomical sites and the longitudinally extending surgical rod. This difficulty can be appreciated when it is realized that a plurality of spaced-apart anatomical sites are usually necessary to achieve acceptable treatment of spinal deformities and instability. A plurality of anatomical sites necessitate a plurality of orthopaedic coupling devices. An increase in the number of anatomical sites is highly desirable for the simple reason that the load or force upon each such site is reduced, thereby better distributing the force acting upon each selected site as well as the force acting upon each section of the elongated surgical rod to which the orthopaedic device is attached. The necessity of manually manipulating a long surgical rod into the bores of a number of different hooks or screws is a problem of considerable concern.
Recognizing that these surgical implants are installed during open-back surgery, while the patient is under anesthesia, it is important to provide the orthopaedic surgeon with implants that are easily and securely installed without risk of undesired slippage along, or rotation about, the surgical rod. When it becomes necessary to remove an orthopaedic device, whether hook or screw, or to reposition the same, it is important that this procedure be achieved within the shortest time possible and with assurance that the repositioned implant will be maintained in its correct position with security. As the very nature of the surgical operation places the surgical rod under stress, as by resisting deforming forces of the spine, it will be appreciated that secure and rigid attachment of orthopaedic implant devices to the surgical rod is a paramount necessity.
The present invention introduces an orthopaedic device achieving improved mechanical coupling to a cylindrical rod. The device can be readily installed upon, positioned along, repositioned, and removed from the surgical rod with a minimum of manual manipulation. The device consists of separate first and second members designed for mechanical interlocking, one within the other. The first member is T-shaped and includes a short, hollow, cylindrical sleeve portion having upper and lower ends and a threaded rod portion extending perpendicularly from the outer surface thereof midway between the upper and lower ends. The threaded rod portion is bisected by a narrow slot which also extends through the outer surface of the hollow sleeve portion, the narrow slot lying in a plane defined by the axes of the hollow sleeve portion and the threaded rod portion. The hollow sleeve portion of the T-shaped member is adapted for slidably receiving the cylindrical surgical rod, and the bisected, threaded rod is adapted for receiving a locking nut. The diameter of the bisected, threaded rod portion is dimensioned to be less than the outer diameter of the hollow sleeve portion.
The second member is generally block-shaped and includes a centrally located cylindrical bore extending therethrough between upper and lower surfaces. A longitudinal slot extends between the upper and lower surfaces and from the front surface through the block into the central bore. The width of the longitudinal slot is made less than the diameter of the cylindrical bore. The diameter of the cylindrical bore is chosen to slidably receive the hollow cylindrical sleeve portion, and the width of the longitudinal slot is dimensioned to slidably pass the bisected rod portion of the T-shaped member. A U-shaped cutout, extending from the middle of one of the side surfaces of the block member and through the block member into the central bore, provides an open yoke into which the bisected rod portion of the T-shaped member may be placed. A locking nut, threaded upon the bisected, threaded rod portion but not tightened, mechanically interlocks the T-shaped member within the central bore of the block-shaped member while permitting the two interlocked members to be slidably positioned along the surface of the surgical rod. When the interlocked assembly is properly positioned at the selected anatomical site, advancing the locking nut further upon the bisected, threaded rod portion creates a force squeezing the narrow slot of the T-shaped member to clamp the hollow sleeve portion upon the cylindrical surface of the surgical rod while holding the T-shaped member firmly and rigidly within the block-shaped member. The block-shaped member will include an appropriate anchor attachment member for attachment to a selected vertebra.
Accordingly, a principal object of the present invention is to provide an orthopaedic device capable of achieving a more secure and rigid coupling to a cylindrical surgical rod.
Another object is to provide an improved orthopaedic device that is both easier and faster to attach to, position along, or be detached from, a surgical rod during the course of the surgical operation.
A further object is to provide an improved orthopaedic device consisting of two separate and interlocking members for simplifying the procedural steps required to achieve mechanical intercoupling between the orthopaedic device and a surgical rod.
The above objects of and the brief introduction to the present invention will be more fully understood, and further objects and advantages will become more apparent, from a study of the following detailed description in connection with the drawings.